a. Field of the Invention
This invention pertains generally to photodiodes, and more particularly to a photodiode device having a high photon-to-electron conversion (quantum) efficiency.
b. Description of the Related Art
A paper entitled "Silicon photodiode device with 100% external quantum efficiency" by Edward F. Zalewski and C. Richard Duda, Applied Optics 22, No. 18, 2867-2873, describes a device utilizing four inversion layer photodiodes in a light trapping arrangement which is said to have a photon-to-electron conversion efficiency of 0.999 for short wavelength and low power visible radiation. Three of the four photodiodes are positioned at right angles to each other in a generally U-shaped configuration, with the fourth photodiodes being inclined at an angle of 45.degree. to the third diode in the group. Radiation impinging upon the first diode in the group at an angle of 45.degree. from the normal is reflected around the group toward the fourth diode where it is reflected back around the group along the same path. While this device provides a relatively high quantum efficiency, it is sensitive to polarization and to the angle of incidence of impinging radiation, and it has a relatively small angle of acceptance (f/22 or more).
It is in general an object of the invention to provide a new and improved photodiode device having a high quantum efficiency.
Another object of the invention is to provide a photodiode device of the above character which can receive impinging radiation over a relatively wide angle of incidence.
Another object of the invention is to provide a photodiode device of the above character which is enclosed and requires no calibration.